1. Field of the Invention
The invention relates to an image forming apparatus provided with cleaning means for electrostatically removing a toner adhering to transferring means.
2. Description of Related Art
In Japanese Patent Application Laid-open No. H11-52757, there is described a construction as shown in FIG. 11 of the accompanying drawings which mechanically clean transferring means.
A toner image formed on a photosensitive drum 101 is primary-transferred to an intermediate transfer belt 107 stretched around a plurality of rollers 102-106, and thereafter is secondary-transferred onto a recording medium by a secondary transfer roller 109. The secondary transfer roller 109 has its shaft 109a supported by a rocking arm 137 which rocks about the center of rocking movement 136. The base end portion of the rocking arm 137 is biased by a tension spring 138, and also is driven by an eccentric cam 139. Thereby, the secondary transfer roller 109 is moved toward and away from the intermediate transfer belt 107. A toner (untransferred toner) adhering to the secondary transfer roller 109 is mechanically wiped off by a cleaning blade 133 brought into contact with the surface of the secondary transfer roller 109.
Also, in Japanese Patent Application Laid-open No. 2001-337542, there is described a construction which, as shown in FIG. 12 of the accompanying drawings, uses electrostatic cleaning for an intermediate transfer belt 208. A toner image formed on a photosensitive belt 201 stretched around rollers 202, 203, 204, and 205 is transferred to the intermediate transfer belt 208 stretched around rollers 209, 210, 211, and 212. Cleaning means 213 is provided on a cleaning area for the intermediate transfer belt 208 formed by a roller 209 as an opposed roller. The cleaning means 213 has a cleaning container 230 fixed to an arm 221 rocking about a shaft 222. In the cleaning container 230, there are disposed a first bias roller 224 and a first fur brush 223 contacting therewith, and a conveying screw 229. A design is made such that the first fur brush 223 and the second fur brush 226 are brought into contact with the intermediate transfer belt 208, and biases of opposite polarities are applied to these to thereby remove a toner on the intermediate transfer belt 208.
However, in the construction described in the above-mentioned Japanese Patent Application Laid-open No. H11-52757, the secondary transfer roller 109 is abraded by the frictional contact of the cleaning blade therewith with the long-term use and therefore, faulty transfer occurs. Also, it is difficult to reliably remove the untransferred toner electrostatically adhering to the secondary transfer roller by the cleaning blade.
On the other hand, in the construction described in Japanese Patent Application Laid-open No. 2001-337542, cleaning biases are applied to the cleaning means and therefore, it is difficult to prevent leakage of the biases to other members and yet, effect good cleaning.
When the cleaning of the transferring means is not effected sufficiently, there occurs the so-called back contamination in which the toner adheres to the back of the recording medium.